The invention relates to a flat diaphragm for use in a magnetic speaker, and more particularly to a flat diaphragm which is formed by a flat, thin sheet of wood plate having a straight-grain or cross-grain on its surface, the specific gravity of which is in the range of 0.25 to 0.8.
Paper formed in a cone shape, made from pulp, has been frequently used in a magnetic speaker (hereinafter referred to as a speaker) diaphragm, and a honeycomb construction has been used to build the flat diaphragms. Core materials for known flat diaphragms have been selected from light metals like aluminum, carbon filter reinforced plastics (CFRP), and glass fiber reinforced plastics (GFRP).
Conventionally, pulp formed into cone paper has been widely used to make speaker diaphragms because its internal friction and specific gravity are suitable for use in speakers, and the material is inexpensive. A disadvantage is that cone paper, made from pulp, lacks rigidity.
Additional disadvantages include space requirements that are large and the occurrence of a frequency turbulence characteristic, known in the industry as "front cell efficiency", generated by air resonance in the concave portion of a cone paper diaphragm. Therefore, material and construction improvements in a speaker diaphragm require the elimination of these disadvantages.
While flat honeycomb constructed diaphragms whose core material is either a light metal, like aluminum, or FRP, have less turbulent frequency characteristics than diaphragms described above, the honeycomb constructed cells resonate with each other causing turbulence within a speaker. The generated resonance may be reduced by making cells smaller, but this involves high manufacturing costs.